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[Asia Economy Reporter Junho Hwang] A technology has been developed to control the orientation of organic polymers using the coffee stain effect, which is easily observed in daily life. This technology is expected to contribute to the development of flexible devices for the Internet of Things (IoT) by enabling the orientation of polymer aggregates in various directions.

The National Research Foundation of Korea announced on the 17th that Professors Dongki Yoon, Hyungsu Kim, and Bongsu Kim from the Korea Advanced Institute of Science and Technology (KAIST) have developed a technology to control the orientation of semiconductor polymer structures using coffee rings. The results of this research were recently published in the international journal ACS Nano. Orientation refers to rod-shaped molecules being arranged in a certain direction. The more aligned in one direction, the higher the degree of orientation. The optical and electrical properties of the structure vary depending on the orientation.

Formation of Polymer Assemblies with Orientation Controlled by Microchannel Width

The research team observed that the orientation of semiconductor polymers changes according to the diffusion rate of the solvent through an organic semiconductor solution. They filled the space between micro-scale (㎛) walls made of a material permeable only to the solvent with the organic semiconductor solution and conducted experiments by varying the gap between the walls to 5㎛ and 10㎛. As a result, they confirmed that the orientation of the long-chain semiconductor polymers changed to vertical or horizontal directions relative to the walls depending on the solvent diffusion rate. Specifically, when the gap between the walls was narrow and the solvent diffusion rate increased, solvent absorption also accelerated, causing the organic polymers to align perpendicularly to the walls.

The transistors fabricated using this method exhibited high electrical anisotropy, which governs charge mobility. This is because the actual distance between polymer chains, where charges can move efficiently, became closer depending on the direction in which the polymer chains were aligned.

The research team stated, "This study demonstrated that polymer aggregates can be oriented in various directions, not just in a single direction as with conventional organic semiconductor polymers," adding, "It is expected to contribute to future applications in display devices, optical devices, and chemical sensors utilizing organic semiconductors."

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